Thermostatic switch with rocking bridging contact



July 5, 1966 R. M. MORRIS 3,259,721

THERMOSTATIC SWITCH WITH ROCKING BRIDGING CONTACT Filed March 19, 1964 2 Sheets-Sheet 1 FIG. 4

INVENTOR. l2 REXFORD M. MORRIS BY M, l6 MYsZWfiu ATTORN EYS July 5, 1966 R. M. MORRIS 3,259,721

THERMOSTATIC SWITCH WITH ROCKING BRIDGING CONTACT Filed March 19, 1964 2 Sheets-Sheet 2 F|G.5 32 33 ill g 5| INVENTOR. REXFORD M- MO RRIS ATTORNEYS United States Patent 3,259,721 TIERMOSTATIC SWITCH WITH ROCKING BRTDGING CONTACT Rexford M. Morris, Mansfield, Ohio, assignor to Therm- O-Disc, Incorporated, Mansfield, Ohio, a corporation of Ohio Filed Mar. 19, 1964, Ser. No. 353,115 Claims. (Cl. 200138) This invention relates to thermostatic controls and more particularly to a new and improved thermostatic control embodying a switch having spaced fixed contacts and a bridging contact member therebetween.

Heretofore, it has been customary in table appliances such as perculators, fryers, heating pans, and the like, where a relatively small thermostatic control is used to provide such control with switch means including a cantilever mounted flexible arm carrying at its extremity a movable contact member engageable with a fixed contact member. The inherent advantage of this type of switch construction was that the entire potential through the switch was across the two contact members. However, due to the characteristics of the flexible contact carrying arm, the capacity of such a switch was necessarily limited to relatively low currents and thus the control was restricted in its use.

Where small thermostatic controls were desired or required, capable of high current carrying capacity, the switch used in such devices was of the bridging contact type. Such switches embodied spaced fixed contact members with a movable bridging contact member spanning the space therebetween. The bridging contact member was normally maintained in contact with the rfixed contacts by spring pressure directed on the bridging contact member at a point intermediate the fixed contacts. In opening the switch the bridging member is lifted or separated from both fixed contact members simultaneously. The advantagesof such a construction from a current capacity standpoint are outweighed by inherent undesirable operational characteristics, principally failures due to open circuit conditions when the switch is in the closed position. The fact that the potential of the switch when 'open is widely separated and the tendency of extraneous matter within the control, to prevent the bridging contact member from effectively engaging the lfixed contact members contribute to open circuit condition.

It is among the objects of the present invention to provide a new and improved thermostatic control embodying switch means of the bridging contact member type, relatively small in size and having high current carrying capacity which overcomes the drawbacks and undesirable features of prior devices of comparable size, and which is simple in manufacture and uniform and consistant in operation within a predetermined temperature range.

Another object of the invention is to provide a thermostatic control incorporating therein switch means of the bridging contact type having the desirable characteristics of a switch including a cantilever mounted contact carrying arm capable of handling relatively high current and being of comparatively small size.

A further object of the invention is to provide switch means for .a thermostatic control having spaced fixed contact members and a freely movable rigid bridging contact member spanning the space the-rebetween, which bridging member is maintained in contact with one of the fixed contacts during all stages of operation of the switch elements.

A further object of the invention is to provide .a thermostatic control device embodying switch means having spaced fixed contact members and a freely movable rigid bridging contact member therebetween wherein the entire potential through the control is across the bridging contact and one of the fixed contacts.

A still further object of the invention is to provide a thermostatic control device embodying switch means having spaced fixed contact members and a movable rigid bridging contact member therebetween wherein the bridging contact is resiliently held in engagement with one of the fixed contact members while being moved with respect to the other of said fixed contact members.

These and other objects and advantageous features of the invention, not at this time more particularly pointed out, will become more apparent as the nature of the invention is better understood from the following detailed description taken in conjunction with the accompanying drawings wherein like reference characters denote corresponding parts and wherein:

FIGURE 1 is a side elevational view of a thermostatic con-tr-ol embodying the present invention,

FIGURE 2 is a top plan view of the device of FIG- URE 1,

FIGURE 3 is a longitudinal sectional view on an enlarged scale taken on the line 33 of FIGURE 2 illustrating the elements of the switch in closed position,

FIGURE 4 is a view similar to FIGURE 3 illustrating the elements of the switch in open position,

FIGURE 5 is a top plan view of the device shown in FIGURE 4 with the cover plate removed to show the interior of the housing and the relative position of the switch elements therein, and

FIGURE 6 is a vertical sectional view taken along the line -66 of FIGURE 5.

With reference to the accompanying drawings, there is illustrated a thermostatic control device incorporating therein switch means of the bridging contact type embodying the present invention and comprising a substantially cylindrical housing 10 having a side wall portion '11 and a bottom wall portion 12 made preferably of an electrical insulating material, heat resistant to a fair degree, such as a phenolic condensation product. Integrally formed with the side wall portion 11 at the upper end thereof and projecting outwardly at diametrically opposite sides of the housing 10 are substantially rectangular portions 16 and 14 which serve as means for effectively separating the terminal elements of the switch a substantial distance from grounded members of the control. The bottom wall 12 is formed with a circular offset extending inwardly from the periphery thereof defining a horizontal wall portion 15 and a continuation 16 of the side wall portion 11.

Extending through the bottom wall 12 is a centrally disposed circular opening 117 for slidably receiving a cylindrical bumper member 18 of suitable insulating material formed with a rounded upper end 19 arranged to engage and actuate the switch element to be hereinafter described. The bumper member 18 is formed with a rounded lower end 20 which is normally disposed below the surface of the bottom wall 12 (FIGURE 3) and is positioned to be engaged and actuated by the central portion of a disc shaped compo-site thermo plate 21. The thermo plate 21 may be a composite bi-metallic snap-acting thermostatic element being characterized in that its central portion has one position of stable equilibrium when cold and another relatively stable position of equilibrium when hot, such positions being of opposite concavity. As illustrated in FIGURE '3, the thermostatic element 21 is shown when the switch elements are in closed position and having an outward curvature, and in FIGURE 4, the element is illustrated in the position of opposite curvature and the switch elements are in open position. In the latter position the bi-metall-ic element is engaged by the lower end 20 of the cylindrical bumper member 18.

The switch housing 10 is provided with a cover member 22 of the same electrical insulating material of which the housing is formed. The peripheral edge of the cover is formed with an annular groove 23 which receives a complementary annular peripheral portion 24 formed on the top edge of the housing 10. Suitable studs 25 extending through openings 26 in the cover member 22 and threaded into the housing 10 serve to maintain the cover in position on the housing.

For securing the bimetallic disc 21 in operating position with respect to the outer surface of the bottom wall 12 there is provided a cup shaped metal case 27 presenting a substantially cylindrical side wall 28 which extend-s snugly around the side wall 11 of the housing. The side wall 28 of the case is formed with a laterally inturned portion 29 which snugly engages the horizontal wall portion 15 of the housing and then continues downwardly in engagement with the continuation 16 of the housing side wall 11 and terminates in a horizontal wall 30 spaced from the lower surface of the bottom wall 12 of the housing 11 to define a circular recess for receiving and confining the peripheral edge of the bi-metallic member 21. The wall 30 is formed with a circular opening 31 to expose the bi-metallic disc to the surrounding ambient temperature. The central portion of the bi-metallic disc 21 freely moves between its positions of opposite concavity in response to temperature changes and serves to move the bumper member 18 from its first position as shown in FIGURE 3 to its second position as shown in FIGURE 4. As shown in FIGURE 5, the outer surface of the side wall 11 is provided with diametrically opposed vertical grooves 32 which are arranged to receive inwardly formed complementary wall portions 33 formed on the side wall 28 of the case 27. The interengagement of the grooves 32 and wall portions 33 serves to secure the metal case and phenolic housing. I

The housing 10 is provided with a substantially rectangular diametrically disposed cavity'extending downwardly from the top surface thereof and defining a switch chamber 34. Each end of the chamber 34 terminates in a transverse slot 34a which receives the body portion 37 of an angulated terminal member 35 formed with a horizontal leg member 36 of reduced width which extends into the chamber and seats on the bottom wall thereof. A continuation portion 38 of the body portion 37 extends over the surface of the rectangular ears or portions 13 and 14 and then may take any desired angulated position depending upon the mounting of the thermostatic control in the environment of the appliance with whichit is used. The leg members 36 of the terminals 35 are secured in the bottom wall of the chamber 34 by means of rivets 39 extending through openings 40 therein and through bores 41 into counter bores 42 formed in the bottom wall 12 of the housing. The rounded head portions of the rivets 39 at opposite ends of the chamber 34 serve as fixed contact members 43 and 44. Spanning the space between the fixed contact members 43 and 44 and extending longitudinally of the switch chamber 34 is a rigid rectangular bridging contact member 46. That end of the bridging contact 46 adjacent to the fixed contact member 43 is provided with upstanding corner tabs 47 at opposite sides thereof.

Adjacent oneend of the chamber 34 the opposed side walls thereof are provided with opposed arcuate grooves 48 and 49. These side wall portions or grooves 48 and 49 cooperate to define a chamber to receive a coil spring 50 one end of which bears against the lower surface of cover 22 and the other end engages the upper surface of the bridging contact member 46 between the upstanding tabs 47. The pressure or bias exerted by the coil spring 50 upon the briding contact member 46 is at a point between the center of the fixed contact member 43 and the midpoint between the fixed contacts 43 and 44; thus the spring member is effective to exert sufficient pressure on the bridging member 46 to normally maintain same in engagement with both of the spaced contact members 43 and 44 (FIGURE 3). However, when the bridging contact member 46 is subject to the upward movement of the end 19 of the bumper member 18 to separate the same from the fixed contact members 43 and 44, the bias of the spring 50 will maintain the end of the bridging contact member 46 in engagement with the fixed contact member 43, permitting it to slide or rock on the dome like upper surface thereof. Thus, the potential of the switch is broken only across the contact surface of the bridging member 46 and the surface of the contact member 44.

Adjacent the end of the chamber 34 in which contact member 44 is mounted the side walls thereof are cut away to define recesses 51 and 5 2 on opposite sides of the switch chamber 34. The recesses 51 and 52 serve as chambers in which flashing or arcing may be expended when contact is made or broken between the bridging contact member 46 and the dome like surface of the contact member 44.

In the operation of the thermostatic control device hereinabove described the normal condition of the bimetallic disc 21 is as shown in FIGURES with the end 19 of the bumper member 18 spaced from the lower surface of the bridging contact member 46, thus the elements of the switch of the device are in a closed position. In this position the spring 50 biases the bridging contact member 46 into engagement with the spaced fixed contact members 43 and 44.

When the control and the bi-metallic disc 21 mounted therein is subjected to a predetermined temperature, the central portion of the disc 21 snaps from the position as shown in FIGURE 3 to a position of opposite concavity as shown in FIGURE 4 whereby bumper 18 is forced against the lower surface of the bridging contact member 46 and acts against the force supplied by the bias of the coil spring 50. The end of the bridging contact member 46 is rocked on the surface of the contact member 43 moving the opposite end of the bridging contact.

to break its engagement with the fixed contact member 44.

When the bi-metallic disc 21 is subjected to a predetermined change in temperature the central portion thereof snaps back to the position shown in FIGURE 3 and the bumper 18 is released from engagement with the bridging contact member 46. The bias being continuous- 1y supplied by spring 50 is suflicient to bring the end of the bridging contact member 46 into engagement with the contact member 44 and close the circuit thereacross. Should any extraneous matter become disposed on the surface of the contact member 44, the potential across the bridging contact and the contact member 44 is suflicient to remove the same by burning or flashing.

Having thus described my invention so that those skilled in the art may understand and practice same, what I desire by Letters Patent is embodied in the appended claims:

1. A thermostatic control device comprising a housing defining an elongated switch chamber, switch means mounted within said chamber and including spaced fixed contact members, one positioned at each end of said switch chamber and a substantially rigid bridging contact member within said chamber adapted to have one side engage simultaneously both of said fixed contact members, spring means disposed in one end of said switch chamber biasing said bridging contact member into said engagement with both of said fixed contact members,

means acting at the center of said bridging contact member in opposition to said last named means for separating said bridging contact member from one of said fixed contact members and rocking said bridging contact member on the other of said contact members while main-' taining contact therewith.

2. A thermostatic control device comprising a housing defining an elongated switch chamber, switch means mounted within said chamber and including fixed contact members one positioned adjacent each end of said switch chamber and a substantially rigid bridging contact member within said chamber spanning the space between said fixed contact members with one side thereof simultaneously engaging both of said fixed contact members, spring means disposed in one end of said switch chamber for normally maintaining said bridging contact member in engagement with said fixed contact members, a bi-metallic disc having two positions of concavity, said disc upon movement from one position of concavity to the other position adapted to act at the center of said bridging contact member to overcome said last means and separate said bridging contact member from one of said fixed contact members and rock said bridging contact member on the other of said fixed contact members while maintaining contact therewith.

3. A thermostatic control device comprising a housing, a substantialy rectangular switch chamber disposed therein, switch means mounted within said chamber including fixed contact members one positioned at opposite ends of said switch chamber and lying in substantially the same plane and a substantially rigid bridging contact member adapted to span the space between said fixed contact members and simultaneously engage the same, spring means disposed in one end of said switch chamber engaging one end of said bridging contact member for maintaining said bridging contact in engagement with both of said fixed contact members at the same time, means including a bi-metallic snap acting disc for exerting pressure at the center of said bridging contact member in opposition to said spring means for separating said bridging contact member from one of said fixed contact members and rocking said bridging contact member on the surface of the other of said contact members.

4. A thermostatic control device comprising a housing defining an elongated switch chamber, switch means mounted within said chamber including spaced fixed contact members one at each end of said switch chamber, a substantially rigid bridging contact member within said chamber adapted to have one surface thereof engage said fixed contact members simultaneously, spring means disposed in one end of said switch chamber adapted to exert pressure on said bridging contact member at a point between the center thereof and the point of engagement with the fixed contact member to resiliently hold said bridging contact member in engagement with both of said fixed contact members simultaneously, means acting at the center of said bridging contact member in opposition to said spring means for moving the same from one of said fixed contact members and rocking said bridging contact member with respect to the other of said contact members while maintaining contact therewith.

5. A thermostatic control device comprising a h0us-.

ing defining an elongated switch chamber therewithin, switch means mounted within said chamber including longitudinally spaced fixed contact members positioned at one end and on the bottom of said switch chamber and a substantially rigid bridging contact member within said chamber adapted to have one side thereof engage simultaneously both of said fixed contact members, spring means adjacent one end of said chamber and engaging one end of the bridging contact member for biasing said bridging contact member into said simultaneously engagement with said fixed contact members, means acting at the center of said bridging contact member in opposition to said last named means for rocking said bridging contact member with respect to one of said contact members while maintaining contact therewith.

References Cited by the Examiner UNITED STATES PATENTS 1,669,608 5/1928 Forshee 200138 2,501,155 3/1950 BOleSky 200ll3 2,671,836 3/1954 Anger et al. 20016 2,694,121 11/1954 Vander Pyl 200138 X 2,951,916 9/1960 Schelfer 20016 2,954,447 9/1960 Bolesky 2001 13 BERNARD A. GILHEANY, Primary Examiner.

L. A. WRIGHT, T. D. MACBLAIN, Assistant Examiners. 

5. A THERMOSTATIC CONTROL DEVICE COMPRISING A HOUSING DEFINING AN ELONGATED SWITCH TRANSFER CHAMBER THEREWITHIN, SWITCH MEANS MOUNTED WITHIN SAID CHAMBER INCLUDING LONGITUDINALLY SPACED FIXED CONTACT MEMBERS POSITIONED AT ONE END AND ON THE BOTTOM OF SAID SWITCH CHAMBER AND A SUBSTANTIALLY RIGID BRIDGING CONTACT MEMBER WITHIN SAID CHAMBER ADAPTED TO HAVE ONE SIDE THEREOF ENGAGE SIMULTANEOUSLY BOTH OF SAID FIXED CONTACT MEMBERS, SPRING MEANS ADJACENT ONE END OF SAID CHAMBER AND ENGAGING ONE OF THE BRIDGING CONTACT MEMBER, MEANS ACTING AT BRIDGING CONTACT MEMBER INTO SAID SIMULTANEOUSLY ENGAGEMENT WITH SAID FIXED CONTACT MEMBER, MEANS ACTING AT THE CENTER OF SAID BRIDGING CONTACT MEMBER IN OPPOSITION TO SAID LASE NAMED MEANS FOR ROCKING SAID BRIDGING CONTACT MEMBER WITH RESPECT TO ONE OF SAID CONTACT MEMBERS WHILE MAINTAINING CONTACT THEREWITH. 